import 'dart:convert';
import 'dart:typed_data';

import 'package:halkyon_learn_flutter/src/feature/pdf_source/data/pdf_engine.dart';
import 'package:material_ui/material_ui.dart';

/// A [PdfEngine] without PDFium, which `flutter test` can't load. A PDF's
/// bytes say what it holds: `pages:12` its page count (10 without), and
/// `chapter:<page>:<title>;` each chapter. Its viewer shows "Page N of M"
/// and does what it is asked at once; [select] plays a selection.
class FakePdfEngine() implements PdfEngine {
  /// The viewers built, the last one showing.
  final viewers = <FakePdfViewer>[];

  /// The regions drawn, in order.
  final rendered = <({int page, Rect region})>[];

  /// What [PdfDocumentView.renderRegion] gives: a PNG's bytes.
  Uint8List image = Uint8List.fromList(const [137, 80, 78, 71, 1, 2, 3]);

  /// Whether the next PDF opened can't be read.
  bool failNext = false;

  /// Selects [text] in the viewer showing.
  void select(String text) =>
      viewers.last.controller.report(selectedText: text);

  @override
  Future<PdfDocumentView> open(Uint8List bytes) async {
    final text = latin1.decode(bytes, allowInvalid: true);
    if (failNext || !text.startsWith('%PDF-')) {
      failNext = false;
      throw const FormatException('Not a PDF.');
    }
    final pages =
        int.tryParse(
          RegExp(r'pages:(\d+)').firstMatch(text)?.group(1) ?? '',
        ) ??
        10;
    return _FakeDocument(this, pages, [
      for (final match in RegExp(r'chapter:(\d+):([^;]+);').allMatches(text))
        (title: match[2]!, page: int.parse(match[1]!)),
    ]);
  }
}

class _FakeDocument(
  final FakePdfEngine _engine,
  final int _pages,
  final List<PdfChapter> _chapters,
) implements PdfDocumentView {
  @override
  int get pageCount => _pages;

  @override
  Future<List<PdfChapter>> chapters() async => _chapters;

  @override
  Future<Uint8List?> renderRegion(int page, Rect region) async {
    _engine.rendered.add((page: page, region: region));
    return _engine.image;
  }

  final _viewers = <PdfReaderController, FakePdfViewer>{};

  @override
  Widget viewer(PdfReaderController controller) {
    // One viewer per controller, however often the reader is built.
    final viewer = _viewers.putIfAbsent(controller, () {
      final viewer = FakePdfViewer(controller, _pages);
      _engine.viewers.add(viewer);
      return viewer;
    });
    return _FakeViewerWidget(viewer);
  }

  @override
  Future<void> dispose() async {}
}

/// The fake viewer's handle: pages 1000 high, 700 wide, one below the other.
class FakePdfViewer(final PdfReaderController controller, final int pages)
    implements PdfViewerHandle {
  /// The texts searched for, in order.
  final searched = <String>[];

  @override
  Future<void> goToPage(int page) async =>
      controller.report(page: page.clamp(1, pages));

  @override
  Future<void> zoomIn() async =>
      controller.report(zoom: controller.zoom * 1.25);

  @override
  Future<void> zoomOut() async =>
      controller.report(zoom: controller.zoom / 1.25);

  @override
  Future<void> fitWidth() async => controller.report(zoom: 1);

  @override
  Future<void> fitHeight() async => controller.report(zoom: 0.5);

  @override
  Future<void> setZoom(double zoom) async => controller.report(zoom: zoom);

  @override
  void search(String text) {
    searched.add(text);
    controller.report(matchCount: 3, currentMatch: 0);
  }

  @override
  Future<void> nextMatch() async => controller.report(
    currentMatch: ((controller.currentMatch ?? -1) + 1) % 3,
  );

  @override
  Future<void> previousMatch() async => controller.report(
    currentMatch: ((controller.currentMatch ?? 1) + 2) % 3,
  );

  @override
  void clearSearch() => controller.report(matchCount: 0, noMatch: true);

  @override
  Rect? pageRect(int page) =>
      Rect.fromLTWH(0, (page - controller.page) * 1000.0, 700, 1000);
}

class const _FakeViewerWidget(final FakePdfViewer _viewer)
    extends StatefulWidget {
  @override
  State<_FakeViewerWidget> createState() => _FakeViewerWidgetState();
}

class _FakeViewerWidgetState() extends State<_FakeViewerWidget> {
  @override
  void initState() {
    super.initState();
    widget._viewer.controller.addListener(_changed);
    // As pdfrx's viewer, ready once laid out.
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (mounted) {
        widget._viewer.controller.attach(widget._viewer);
      }
    });
  }

  @override
  void dispose() {
    widget._viewer.controller
      ..removeListener(_changed)
      ..attach(null);
    super.dispose();
  }

  void _changed() => setState(() {});

  @override
  Widget build(BuildContext context) => ColoredBox(
    color: const Color(0xffdddddd),
    child: Center(
      child: Text(
        'Page ${widget._viewer.controller.page} of ${widget._viewer.pages}',
      ),
    ),
  );
}